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Synthesis of Rosin-based Surfactants


Classification of surfactants based on the charge characteristics of their polar (hydrophilic) head groups is commonly used. Like other surfactants, rosin-based surfactants can be classified into four groups: cationic, anionic, zwitterionic and nonionic. Cationic surfactants are those that have a positive charge on their polar head group. Anionic surfactants are those that have a negative charge on their polar head group. Zwitterionic surfactants have the potential to have both positive and negative charges, depending on the environment in which they are placed. Nonionic surfactants have no charge on their head group.

The majority of rosin-based cationic surfactants are quaternary ammonium compounds, in which the nitrogen atom carries a positive charge.There are two methods to prepare rosin-based quaternary ammonium compounds. One is to quaternise a tertiary amine with a halide and most rosin-based cationic surfactants are synthesised by this method. The other is to graft rosin derivatives with active quaternary ammonium salts. There are two kinds of rosin-based cationic surfactants. One is an ester quaternary ammonium surfactant and the other, a dehydroabietylamine-derived quaternary ammonium surfactant.


The most widely used starting materials for the synthesis of rosin-based quaternary ammonium compounds are rosin amine or dehydroabietylamine. Rosin amine or dehydroabietylamine can be used as starting materials to prepare tertiary amine in the presence of formaldehyde and formic acid, and then the rosin based quaternary ammonium salts can be prepared in a standard procedure called quaternisation.


Rosin acids can be changed into acid chlorides, salts and amines, which greatly improve the reactivity. The most common nonionic surfactants are those based on ethylene oxide and are referred to as ethoxylated surfactants. Several classes can be distinguished: rosin acid ethoxylates, rosin alcohol ethoxylates, monoalkanolamide ethoxylates and rosin amine ethoxylates. The other kind of rosin-based nonionic surfactant is a sugar-based surfactant; in which glucose and sucrose were introduced to the basic skeleton of rosin. Another important class of nonionic surfactant comprises multihydroxyl products such as glycol esters and poly glycerol esters.


Rosin-based cationic surfactants exhibited corrosion inhibition activity. Inhibition of metal corrosion by organic compounds is a result of the adsorption of organic molecules or ions at the metal surface forming a protective layer. This layer reduces or prevents corrosion of the metal. The extent of adsorption depends on the nature of the metal, the metal surface condition, the mode of adsorption, the chemical structure of the inhibitor, and the type of corrosion medium.


The advantages of rosin-based surfactants as a chiral surfactant for the separation of amino acids are that the tricyclic hydrophenanthrene structure contains many chiral centres, the synthetic procedure for the surfactants is relatively simple and the starting material is a natural product which easily available.